Money or currency, sometimes called legal tender was a medium of exchange used to facilitate transactions of goods or services. (TNG: "Time's Arrow") Societies that used money were described as practicing currency-based economics. (DS9: "In the Cards")

In 2364, Jean-Luc Picard tried to explain to Ralph Offenhouse, a financier from the 20th century, that there would be no need for his services any longer. "A lot has changed in three hundred years," said Picard. "People are no longer obsessed with the accumulation of 'things.' We have eliminated hunger, want, the need for possessions." (TNG: "The Neutral Zone")

When Lily Sloane asked Picard how much the USS Enterprise-E had cost to build, he told her, "The economics of the future is somewhat different. You see, money doesn't exist in the 24th century... The acquisition of wealth is no longer the driving force in our lives. We work to better ourselves and the rest of Humanity." (Star Trek: First Contact)

When Nog suggested that Jake should bid for a baseball card in an auction in 2373, Jake said, "I'm Human, I don't have any money." Nog commented, "It's not my fault that your species decided to abandon currency-based economics in favor of some philosophy of self-enhancement." Jake answered, "Hey, watch it. There's nothing wrong with our philosophy. We work to better ourselves and the rest of Humanity." Nog then replied, "What does that mean?" Jake responded, "It means... It means we don't need money!" Nog quickly pointed out, however, that Jake wouldn't be able to bid or borrow. (DS9: "In the Cards")

Outside of Earth, money and other forms of currency were still used in the 23rd and 24th century: by the Federation itself, individual Humans and other Federation species. One form of such currency was the Federation credit.

That same year, while playing the role of the title character in a Dixon Hillsimulation, Picard stated a rate of $20 a day plus expenses to Jessica Bradley, who was convinced that someone was trying to kill her. She accepted and gave him a "c-note," or $100, as an advance. Later in the simulation, he wished to purchase a newspaper but did not have any money, and was told by the vendor that he could catch him next time. (TNG: "The Big Goodbye")

As Star Trek generally has established that in the Federation, poverty, hunger, etc. have been eradicated among member planets, it would seem that the term "starving" must be relative.

While inside the Nexus, Kirk described an illusion to Picard, remarking, "It's my house... I sold it years ago." Kirk was actually referring to a former home of his on Earth. (Star Trek Generations)

In 2374, a smiling Jake Sisko mentioned to Quark that he had "sold [his] first book" earlier that day. Seemingly surprised, Quark asked Jake how much he had acquired from the sale of the book, to which Jake further explained, "It's just a figure of speech. The Federation News Service is going to publish a book of my stories about life on the station under Dominion rule." Jake then confirmed that he had not been paid. (DS9: "You Are Cordially Invited")

In the final draft script of TOS: "Charlie X", Doctor McCoy jokingly told Captain Kirk that, if McCoy was permitted to "just sit quietly in the background and hear" Kirk give Charles Evans a disciplinary talk, he "would gladly give up a year's pay."

The final draft script of TOS: "Miri" implied that the society on Earth Two involved money, as a wig scripted to be worn by Jahn was described (in one of the teleplay's stage directions) as having a price tag still attached while the wig was being worn.

Ronald D. Moore commented, "By the time I joined TNG, Gene [Roddenberry] had decreed that money most emphatically did NOT exist in the Federation, nor did 'credits' and that was that. Personally, I've always felt this was a bunch of hooey, but it was one of the rules and that's that." (AOL chat,1997)

A cut scene in the script of Star Trek: First Contact would have established that, as of 2063, "no one" had used currency in ten years, apparently due to scarcity. However, a currency called Dome money was also mentioned.

An ultimately omitted line of dialogue from the final draft script of ENT: "Carpenter Street" featured 21st century Human Loomis exclaiming to 22nd century Vulcan T'Pol, "You act like money doesn't mean anything!"

In the mirror universe of the alternate reality-set comic "Live Evil", James T. Kirk (β) mentions a monetary unit called the "chit".

In the 25th-century timeline of Star Trek Online, a currency system called "Energy Credits" (EC) has achieved near-universal acceptance among galactic powers, including the Klingon Empire and Romulan Star Empire. EC may be exchanged by individuals or traded for goods and services, and many commodities have a fixed EC "cost" to obtain from a replicator. It is implied that EC are intended as a direct representation of the amount of energy used to replicate or construct a given item, allowing commodities to become "cheaper" if they can be created for less energy. It is not known whether EC is used at large in the same way as regular currency, or if it is simply a convenient way for the game to facilitate more traditional economic activity.